Drill Through on Ending Balance Fails with "Could Not Find Period key for given parameters"

Summary:

After loading data to an application in ARCS, I'm getting an error when I drill on the Ending Balance in Reconciliation after the load, screenshot below. I have Period Keys mapped and also I mapped Year and Period for the Reconciliation Compliance Balances to UD columns. Is there a step I'm missing?

Content (please ensure you mask any confidential information):

I'm trying to set up drill through for the Ending Balance amount for a Reconciliation, but after load, it says there is not a Period Key mapping, even though I have Year and Period mapped to UD columns for the application and I have the Period Keys appropriately mapped. Any help would be appreciated.